When animals are experimentally addicted to opiate drugs, behavioral, as well as physiological deficits are often seen. However, behavioral testing usually occurs either just after drug intake or when "withdrawal" is presumed to be maximal. It is not known, however, what effects would be observed if the animals were allowed to self-regulate their drug levels. The present experiment attempts to determine how behavior on standard learning tasks will vary with drug levels and intake procedures. Rats will be addicted to morphine and then tested with 0, 12, or 24 hours between injection and testing. The performance of these animals will be compared with that of animals allowed to self- regulate their own morphine (or methadone) levels via drinking. Behavioral tasks will include active and passive avoidance, conditioned emotional response learning, simple operant behavior and visual discrimination learning. The rationale of drug substitution and maintenance therapy would predict that self-regulating rats would perform better than rats under either quite high or quite low (withdrawal) drug levels.